The present invention pertains to a blade tensioner equipped with a blade shoe having a chain sliding face and several plate-like blade springs for applying a spring force to the blade shoe.
Conventionally, a blade tensioner has been utilized as a tensioner for applying tension to a chain. An example of a prior art blade tensioner is shown in FIG. 9.
As shown in FIG. 9, a prior art blade tensioner 100 may be configured primarily with a resin blade shoe 101 having a curved chain sliding face 101a and several metal blade springs 102 stacked on the reverse side of the chain sliding face 101a of the blade shoe 101 in order to apply a spring force to the blade shoe 101. Respective ends of the plate-spring-like blade springs 102 may be disposed in concave parts 111 and 113 created at a tip part 110 and a base part 112 of the blade shoe 101.
In addition, a bracket 120 for installing the blade tensioner 100 into an engine can be provided. Holes 121 and 122 for inserting attachment bolts may be created on the bracket 120. A sliding face 125 which allows the tip part 110 of the blade shoe 101 to slide while remaining in contact is created at the tip of the bracket 120, and a pin 130 which supports the base part 112 of the blade shoe 101 while allowing it to pivot freely can be fixed near the center of the bracket 120 by one end.
During the operation of the chain, the chain runs while sliding on the chain sliding face 101a of the blade shoe 101. At this time, a pressing load created as the blade shoe 101 and the blade springs 102 are deformed may act upon the chain, so that constant tension of the chain is maintained. In addition, chord vibrations caused by thrashing of the chain and/or fluctuation of tension are propagated to the respective blade springs 102 in the blade shoe 101 via the blade shoe 101. At this time, the adjoining blade springs 102 slide against each other as the respective blade springs 102 are repeatedly subjected to elastic deformation and return deformation, and the chord vibrations of the chain are damped.
The blade springs as products are subject to quite significant variation in terms of curvature and length. Thus, when several of the blade springs are stacked and installed into the blade shoe, as shown in FIG. 10, contact positions C and Cxe2x80x2, contact conditions, and gaps between the respective blade springs 102 may vary.
As a result, the overall damping factor of the blade springs varies, creating a problem that the damping performance of a blade tensioner may vary.
In accordance with an aspect of the invention, a blade tensioner is provided for applying tension to a chain equipped with a blade shoe having a chain sliding face, several plate-spring-like blade springs stacked on the reverse side of the aforementioned chain sliding face of the aforementioned blade shoe in order to apply a spring force to the aforementioned blade shoe, and spacer members provided between the aforementioned adjoining blade springs and brought in contact with corresponding blade springs at at least two points separated from each other by a fixed distance.
During the operation of the chain, the chain runs while sliding on the chain sliding face of the blade shoe. At this time, a pressing load created as the blade shoe and the blade springs are deformed may act upon the chain, so that constant tension is imparted upon the chain.
What is more, in such case, spacer members may be provided between the respective adjoining blade springs, and the spacer members can be brought in contact with the corresponding blade springs at at least two points separated from each other by a fixed distance.
That is, the respective blade springs can be in contact with the spacer members at junctions of a fixed span instead of at irregular contact points. Accordingly, fluctuation of the damping factor of the overall blade spring or system can be reduced or eliminated, so that the damping performance of the blade tensioner can be stabilized.
In an aspect of the blade tensioner of the invention, almost uniform gaps can be created between the aforementioned adjoining blade springs. In such case, when the pressing load is applied by the chain, uneven contact between the deformed blade springs can be avoided. Accordingly, fluctuation of the damping factor of the overall blade spring due to changes in the contact condition can be prevented.
In a further aspect of the blade tensioner of the invention, the aforementioned spacer member may be configured with several spacer parts laid out at certain intervals in the width direction of the spring and a pair of connector parts extending in the length direction of the spring while connecting the aforementioned respective spacer parts.
In such case, because each spacer part functions to serve as a spacer between blade springs, an almost uniform gap can be created between the blade springs along the length direction of the springs due to these spacer parts. Accordingly, the curvature of the respective blade springs can be made almost uniform. As a result, the damping factor of the overall blade spring can be constant, so that the damping performance of the blade tensioner can be stabilized.
What is more, in such case, because almost uniform gaps can be created between the respective adjoining blade springs, the deformed blade springs can uniformly contact the spacer members to be brought into contact with them as the pressing load is applied by the chain. Accordingly, the damping performance of the overall blade spring can be stabilized. In addition, in such case, because the number of contact faces with the spacer members increases, the damping force of the blade tensioner can be improved.
In yet another aspect of the invention, the aforementioned spacer part may have a cross section in the shape of a circle, an oval, or a rectangle.
According to another aspect of the invention, retainer parts for preventing the aforementioned spacer members from falling off the aforementioned blade springs may be created at the ends of the aforementioned spacer parts.
According to yet another aspect of the invention, the aforementioned connector parts may have a retaining function to prevent the aforementioned spacer members from falling off the aforementioned blade springs.
In another aspect of the invention, the aforementioned spacer members may be created by means of molding or press-punching a net band.
In yet another aspect of the invention, contact faces between the aforementioned spacer members and the aforementioned blade springs may be provided with a friction material. In such case, the damping force can be increased by the spacer members; and the damping performance of the blade tensioner can be improved accordingly.